This invention relates to a method for determination of a rigid value of an aerodynamic coefficient of an aircraft.
Throughout the description, the term “aircraft” is used to designate generically a type of aircraft (for example an aircraft known under the name A320 or A319 . . . ) and not a given specimen.
Furthermore, the terms “aerodynamic coefficient” designate in usual manner adimensional coefficients used to quantify the forces or moments exerted by the air in motion on a part or the entirety of the aircraft. Among these coefficients there may be cited, for example, the lift coefficient CZ, the drag coefficient CX, the lateral force (or drift) coefficient CY, the roll moment coefficient CL, the pitch moment coefficient CM, the yaw moment coefficient CN, or else any pressure coefficient making it possible to quantify locally the pressure exerted by the air in motion. The terms “aerodynamic coefficient” here also extend to other characteristic parameters of the aerodynamics of the aircraft, such as the efficacies in lift, in drag, in drift, in roll, in pitch and in yaw of a mobile surface (aileron, spoiler, flap . . . ) of the aircraft. The efficacy in lift (respectively in drag, in drift, etc.) of a mobile surface expresses the impact of the total deflection of this mobile surface on the lift (respectively drag, drift, etc.) coefficient of the aircraft.
It should be noted that the value of an aerodynamic coefficient depends on a set of environmental and operational conditions, including the temperature of the air, the pressure, the speed of the air flow in relation to the aircraft, the angle of incidence . . . . These conditions also may be defined with the aid of basic parameters such as: the Reynolds number Re, which represents the ratio between the inertia forces and the viscous forces (with Re=ρVL/μ=VL/v, where V is the speed of the air flow in relation to the aircraft, L the characteristic length, ρ the voluminal mass of the air, μ the dynamic viscosity of the air and v the kinematic viscosity of the air); the Mach number Ma, which represents the ratio between the speed of the air flow in relation to the aircraft and the speed of sound, etc.
Finally, by “rigid value” of such an aerodynamic coefficient there is understood the theoretical value which this coefficient would assume if the aircraft were perfectly rigid, for the set of environmental and operational conditions under consideration.
The digital calculation models used to dimension the different parts of an aircraft generally bring in rigid values of aerodynamic coefficients. Nowadays there are used in the known digital models, as rigid values of the aerodynamic coefficients of an aircraft, values of the coefficients determined on the basis of results of tests conducted in a wind tunnel on a model of the aircraft, considering that such a model is practically rigid.